Piles are used when they are more economical than the alternatives, or when the ground at foundation level is too weak to support any of the previously described foundation types. Piles are also used on sites where soils are particularly affected by seasonal changes (and/or the action of tree roots), to transfer the structural loads below the level of such inﬂuence. Piles can transfer the structure load to stronger soil, or to bedrock and dense gravel. The structural load is supported by the pile, acting as a column, when it is end-bearing on rock (or driven into dense gravel), or alternatively by skin friction between the peripheral area of the pile and the surrounding soil (similar to a nail driven into wood) or by a combination of both.

Rapid advances in piling technology have made piling on many sites a viable alternative economic proposition and not necessarily a last resort. The reduction in piling costs has also made possible the use of land which previously was considered unsuitable for building. The authors’ practice, for example, economically founded a small housing estate on a thick bed of peat by the use of 20 m long piles to support the low-rise domestic housing. Consideration should also be given to the use of piles on contaminated sites where driven piles can be economic as they do not produce arisings that would otherwise need to be disposed of off site at great cost. Typical examples of piling are shown in Fig. 1.8.